Nasolacrimal duct

As tear duct ( lacrimal Viae ) the anatomical structures of the lacrimal system are called to serve the derivation of the tear fluid formed by the lacrimal glands of the nose. The lacrimal puncta and includes the two canaliculi, the lacrimal sac and the nasolacrimal passage.

In normal production of tears the tear ducts direct the tears into the nose, where it evaporates. Only with increased tear production or disturbance of the drainage system, there is an overflow of tears over the lid margin, which is called (Greek for " epiphora " ) as epiphora.

• 4.1 overproduction of tear fluid
• 4.2 malposition of the eyelids
• 4.3 clogging and narrowing
• 4.4 Congenital stenosis
• 4.5 inflammation
• 4.6 injuries

Structure and function in humans

Membranous lacrimal duct passage

The tear fluid is distributed over the eyelid over the cornea and keeps it moist. It is then discharged via two point-like openings on the nose-side angle of the eye, the upper and lower punctum ( puncta lacrimalia ), from the conjunctival sac with the lacrimal lake ( Lacus lacrimal ). Tear points are equipped with a circular muscle that can close the opening of the tear points ( 0.34 to 0.64 mm).

From these points, each one canaliculi ( canaliculus ) leads first 1.5-2 mm to the vertical and then bends at a sharp bend in the 6-8 mm long horizontal portion from. In general, the upper and lower canaliculi then unite to form a horizontally extending common canaliculi ( lacrimal duct communis), which is regarded as a fine tissue of lacrimal sac ( lacrimal sac ) duly and in which he leads. The lacrimal sac is also in the eye socket, the lower part of the eye in a shallow pit ( lachrymal fossa ) in the lacrimal bone ( lacrimal ). It measures 12 mm in humans, in the vertical direction and about 4 mm in the horizontal and has an average volume of 20 ul. As a " puffiness " is popular also the sagging and droopy skin of the lower eyelids called ( cutis laxa ), optionally in combination with a eyelid by the bulging fat in the eyelids. These have no relationship to the lacrimal apparatus.

The eye ring muscle ( orbicularis oculi ) is mediated via a tendinous structure ( Lidbändchen ), compress the lacrimal sac and thereby create a negative or positive pressure, which forwards the tear fluid aspirates or in the nasolacrimal passage ( nasolacrimal duct ). The nasolacrimal passage is surrounded on all sides by bony structures and flows in humans after a maximum of 5 mm in the inferior meatus. The opening point of the nasolacrimal passage behaves tierartlich - comparing very different. Even within a species can be the mouth in the middle of the lower nasal passage or only in the nasal vestibule, such as in dogs. On the nose, the lacrimal fluid to moisten the nasal mucosa serves and evaporated. A valve mechanism ( Hasner - fold or flap ) prevents the back flow of tears.

The membranous lacrimal duct hose has a multitude of narrow, wrinkles and bays. From top to bottom the following structures are happening:

• Bochdalek - fold
• Rose Müller- fold
• Arlt sine
• Kraus or Berault - fold
• Spiral fold after Hyrtl
• Taillefer - flap
• Hasner - fold ( plica lacrimal ): mucosal fold at the mouth of the nasolacrimal canal

The canaliculi are lined with a stratified squamous epithelium, the remaining lacrimal with a pseudostratified columnar epithelium. Below is loose connective tissue, in which an extensive venous plexus ( plexus ) is embedded. The pulsation of the blood vessels supports the lacrimal drainage.

Boney supporting skeleton of the lacrimal

The upper portion of the bony lacrimal duct passage originating at the lacrimal fossa ( fossa sacci lacrimal ), which is bounded fore and aft by a bony edge ( lacrimal ) of the lacrimal bone ( lacrimal ). In the upper part they are the ethmoid cells, adjacent to the middle meatus in the lower part. On the downside, the tear duct connects whose limits to the side of a channel of the upper jaw bone ( maxilla lacrimal sulcus ) and nose upward by a projection of the nasal bone (Processus lacrimal of Os conchale ) are formed. The back wall is formed in the side portion of one part of the maxillary bone and nose upward from the middle meatus. The tear duct opens into the inferior meatus.

Since the facial skeleton of man can have a very variable form, also vary the dimensions of the bony passage. The length of the pit is slightly tears 16 mm, and 5-6 mm wide, the channel is from 12.4 to 15 mm long. It runs at an angle of 15-25 ° to the "back and to the side " down, so that the channels of both sides soft apart.

Nasolacrimal duct probe seen from the inside, opening out beneath the inferior turbinate

History of development

From an embryo length of about 8 mm tear trough can be detected. It is located on the lateral nasal process and acts as a growth track for the membranous tear ducts. These grow initially as a solid epithelial cords into the mesenchyme.

At the rear end sprouted two hollow strands in the direction of nasenwärtigen canthus. Your adhesions with the Lidrandepithel represent the puncta dar. The distal portion has budded into the inferior meatus. From the 3rd month, the erosion in solid strands begins so. Until 5 -6 Month of development is opened both the puncta as well as access to the nose. The latter step remains the case until the time of birth (see Congenital stenosis) at about 70 %.

Tear ducts in animals

The anatomical structures of the lacrimal ducts of mammals are constructed basically similar. However, there are also differences: thus in some mammals is formed only one punctum (eg rabbits) on each side.

Investigation techniques

The dye test, a colorant is added to the conjunctival sac. In normally functioning tears Because of the dye should be ( about 5 min. ) Removed and can no longer be found in the conjunctival sac after a short time. When Jones test, a dye is also added to the conjunctival sac. The test is referred to as negative if no dye in the duct is found in the nose. This is an indication of obstruction of the lacrimal drainage system.

In the lacrimal duct probing and flushing the tear ducts on passability and finally flushability be examined with a special blunt lacrimal duct cannula. The bony portion of the tear ways can be investigated in this way only in an anesthetized patient.

Of the imaging techniques are mainly the X-ray examination with contrast medium ( Dakryozystographie, DCG ), optionally in digital subtraction and computed tomography ( CT Dakryozystographie ) is important. Magnetic resonance imaging, scintigraphy, ultrasound and endoscopy can be used for special cases also for diagnosis.

Diseases and disorders

Over-production of tear fluid

Only when an excess tear production (for example, due to inflammation of the conjunctiva or in humans emotionally related) the transport capacity of this efferent system is not sufficient and the lacrimal runs over the edge of the eyelid, then " roll the tears " over the face. At the same time there is also an increased volume of fluid in the nasal cavity ( nose drops ).

Malposition of the eyelids

In a deformity of the eyelids outwards ( ectropion ), the punctum no longer plunge into the lacrimal lake. The tear fluid can thus not reach the tear ducts and leads to epiphora. Surgical correction of malposition is required in these cases.

Blockage and narrowing

Even with a congenital ( malformation ) or acquired blockage or narrowing (stenosis ) of the lacrimal drainage pathways, such as bacterial infections or inflammation of the nose ( rhinitis ) with swell up the opening of the nasolacrimal canal, there is a flow of tears over the lid margin. The narrowing can occur in the region of the lachrymal ( präsaccal ) or in the area of ​​Saccusausgangs or nasolacrimal duct ( postsaccal ). If drug therapy is insufficient, the natural tear duct can be surgically restored (such as tear duct endoscopy ) or a bypass (bypass) to create the throat to the nose. In some cases, the implantation of a lacrimal duct prosthesis is required. For all surgical procedures on the lacrimal usually a general anesthetic is required.

Congenital stenosis

In children, sometimes not opening Hasner flap prevents (see above) the removal of Tears (congenital nasolacrimal duct ). In these cases, can be probed with a special blunt tear duct lacrimal cannula and rinsed. Since this procedure is painful, it should be performed under general anesthesia.

Inflammation

Inflammation of the lacrimal sac is called dacryocystitis. Pathologically there is an empyema. It comes to this painful swelling in the area of the lacrimal sac. Sometimes pus drained spontaneously through the skin, in individual cases, the lacrimal sac must be relieved through a stab incision. Antibiotic therapy is usually required. Due to the anatomical proximity to blood vessels that move into the brain ( angular vein ), life-threatening complications can arise. Since in most cases a outflow obstruction is the cause of the inflammation, surgical rehabilitation is ultimately often necessary.

The canaliculi may ignite ( Canaliculitis ) and lead to a painful swelling. Often bacterial infections and / or Tränenwegssteinchen ( Dakryolithen ) are the cause of this. Antibiotic therapy is often required, where appropriate, surgical removal of the Tränenwegssteinchen.

Injuries

In case of violation of the lids to the nasal side of the puncta may lead to the involvement of the lachrymal. A violation of the tear ducts must be detected in time and a surgical repair of canaliculi are carried out, as it can lead to scar healing and loss of function with epiphora otherwise.